Thread: having problem declaring a generic type array in OrderSet class

guys, I have declare a generic array in OrderSet class; however, during compilation is giving me an error:

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.Comparable;
	at wordset.OrderSet.<init>(OrderSet.java:17)
	at wordset.Main.main(Main.java:20)
Java Result: 1

main

public class Main {
 
    public static void main(String[] args) throws IOException
    {
        OrderSet<String> s1 = new OrderSet<>();
 
        String fileName;
        Scanner in = new Scanner(System.in);
 
        System.out.println("Enter the name of the input file");
        fileName = in.next();
 
        File inFile = new File(fileName);
 
        Scanner input;
        try {
            input = new Scanner(inFile);
            while (input.hasNext()) 
            {
                String w = input.next();
                s1.add(w);                
 
            }
        } catch (FileNotFoundException ex) {
           Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);            
        }
 
        s1.show();
 
    } 
 
}

public interface Set<T> {
 
    public void add(T x);
 
    public void show();
 
}

import java.util.Arrays;
 
 
public class OrderSet<T extends Comparable> implements Set<T> {
 
    private T[] items;
    private int size;
 
    public OrderSet()
    {
        items = (T[]) new Object[5];        
    }
 
    @Override
    public void add(T s)
    {
 
        if(size >= items.length)
        {
            items = grow(items);
        }
 
        for (int i = 0; i < items.length; i++) {
            if(items[i] == null)
            {
                items[i] = s;
                size++;
                break;
            }
        }      
 
    }
 
    @Override
    public void show()
    {
        int i = 0;
        while(i < size)
        {            
            System.out.print(items[i]+", ");
            i++;
        }
    }
 
    public T[] grow(T[] a)
    {
        T[] newA = (T[]) new Object[a.length+5];
        System.arraycopy(a, 0, newA, 0, a.length);
        return newA;
    }
 
}

I don't understand that error, but I can tell you that this isn't correct:

OrderSet<String> s1 = new OrderSet<>();

That you can't use empty generic parameter brackets. Better to do:

OrderSet<String> s1 = new OrderSet<String>();

Edit: Please ignore this drivel as it was posted in ignorance. Listen to helloworld922.

Originally Posted by Fubarable

I don't understand that error, but I can tell you that this isn't correct:

OrderSet<String> s1 = new OrderSet<>();

That you can't use empty generic parameter brackets. Better to do:

OrderSet<String> s1 = new OrderSet<String>();

That's actually a new featured of Java 7 (type inferencing for generic object creation). See: Type Inference for Generic Instance Creation

The problem is actually here:

items = (T[]) new Object[5];

You can't cast an Object[] to a T[] since Object is not a T or a subclass of T.